Making the Crumb Topping:

1. Combine Dry Ingredients: In a medium bowl, whisk together all-purpose flour, brown sugar, granulated sugar, cinnamon, and nutmeg (if using).
2. Cut in Cold Butter: Add the cold, cubed butter to the dry ingredients. Use a pastry blender or your fingertips to cut the butter into the dry ingredients until the mixture resembles coarse crumbs and the butter is in pea-sized pieces. Working quickly and keeping the butter cold is key to achieving a crumbly topping.
3. Add Nuts (Optional): If using nuts, stir them into the crumb mixture.
4. Set Aside: Set the crumb topping aside while you prepare the cake batter.

Making the Chocolate Coffee Cake Batter:

1. Preheat Oven and Prepare Pan: Preheat oven to 350°F (175°C). Grease and flour a 9×13 inch baking pan. You can also line the bottom of the pan with parchment paper for easier removal, leaving an overhang on the sides to lift the cake out after baking.
2. Whisk Dry Ingredients: In a large bowl, whisk together all-purpose flour, cocoa powder, baking powder, baking soda, and salt.
3. Combine Wet Ingredients: In a separate large bowl, whisk together granulated sugar, brown sugar, and vegetable oil until combined. Whisk in the eggs one at a time, then whisk in the buttermilk and vanilla extract until smooth.
4. Combine Wet and Dry Ingredients: Gradually add the dry ingredients to the wet ingredients, mixing on low speed with an electric mixer or whisking by hand until just combined. Be careful not to overmix, as this can result in a tough cake.
5. Add Hot Coffee: Gradually pour in the hot brewed coffee (or hot water with instant coffee), mixing on low speed or whisking until just combined. The batter will be thin.
6. Fold in Chocolate Chips (Optional): If using chocolate chips, gently fold them into the batter.
7. Pour Batter into Pan: Pour the batter into the prepared baking pan and spread evenly.
8. Sprinkle Crumb Topping: Sprinkle the crumb topping evenly over the cake batter.

Baking the Cake:

1. Bake: Bake in the preheated oven for 30-35 minutes, or until a toothpick inserted into the center comes out clean or with moist crumbs attached. Baking time may vary depending on your oven. Start checking for doneness around 30 minutes and adjust baking time as needed.
2. Cool: Let the cake cool in the pan for 15-20 minutes before glazing. Cooling allows the cake to set slightly before glazing.

Making the Coffee Glaze (Optional but Highly Recommended):

1. Whisk Glaze Ingredients: While the cake is cooling, prepare the glaze. In a medium bowl, whisk together powdered sugar, hot brewed coffee (or strong hot water with instant coffee), melted butter, vanilla extract, and salt until smooth and creamy. Add more hot coffee, one teaspoon at a time, if needed to reach desired drizzling consistency.
2. Glaze the Cake: Once the cake has cooled slightly, drizzle the coffee glaze evenly over the top of the cake.
3. Let Glaze Set: Let the glaze set for about 15-20 minutes before slicing and serving. This allows the glaze to firm up slightly.

Serving and Storing:

1. Serve: Slice the Chocolate Coffee Cake into squares and serve warm or at room temperature. It’s delicious on its own or with a scoop of vanilla ice cream or whipped cream.
2. Store: Store leftover cake in an airtight container at room temperature for up to 3 days or in the refrigerator for up to 5 days. The cake is wonderfully moist and keeps well.